The present invention relates to a process and apparatus for the continuous manufacture of peroxydicarbonates in high purity.
Peroxydicarbonates, RO-C(O)-OO-C(O)-OR, have recently gained considerable importance as initiators in the polymerization field since they can be used in substantially reduced amounts in comparison to peroxyester initiators, R-C(O)-OO-R. One of the disadvantages of peroxydicarbonates, however, especially in their process of manufacture, is their inherent stability. Peroxydicarbonates such as diisopropylperoxydicarbonate (IPP) and di-n-propylperoxydicarbonate (NPP) are very sensitive both thermally and to heavy shock. Both are capable of detonating under certain conditions. For example, on standing at room temperature IPP decomposes with vigorous gassing and the vapors may autoignite.
The preparation of peroxydicarbonates must therefore be carried out with precautionary measures provided to prevent decomposition from either heat or impact. In commercial batch processes where large amounts are handled in order to be economical, serious explosions have occurred in making pure product. The other alternative has been to use diluents or inert solvents in the process and to sell a dilute product.
For example, U.S. Pat. No. 3,377,373 describes a process for the continuous manufacture of peroxydicarbonates wherein a chloroformate (or chlorocarbonic acid ester) is reacted with hydrogen peroxide and an aqueous alkali metal hydroxide solution in at least two reaction zones, the reaction being terminated in the last or after-reaction zone by addition of a halogenated organic solvent or a liquid halogen-free hydrocarbon solvent. The solvent solution is then isolated by using various settling vessels, washing vessels and the like. A similar continuous process using solvents is described in U.S. Pat. No. 3,429,910.
Since the use of solvents decreases the efficiency of processing and since pure (undiluted) peroxydicarbonates are desired for many polymerization processes, it would be highly desirable to have a continuous, solvent-free process which would increase processing efficiency and be capable of providing the polymerization industry with a choice of either pure or diluted products.